1. Field of the Invention
Embodiments of the invention relate to a surface-controlled subsurface safety valve (SCSSV) and also to an effluent-production installation including such a safety valve. In the meaning of the invention, the term “effluent” is used more particularly to designate oil or gas, but may also apply to other fluids, such as water.
2. Description of the Related Art
SCSSVs are commonly used for shutting-off oil or gas wells. Such SCSSVs are typically installed in a production column in a hydrocarbon production well, and they have the function of blocking the upward stream of fluid formation through the production column in the event of there being a problem or a dangerous condition occurring at the surface of the well.
Typically, SCSSVs are configured so as to be rigidly connected to the production column (accessible in the column) or else they are suitable for being installed and recovered by means of a cable without disturbing the production column (recoverable by cable). During normal production, the subsurface safety valve may be held in the open position by applying hydraulic fluid pressure that is transmitted to an actuator mechanism.
The hydraulic pressure is commonly prepared by means of clean oil coming from a tank of fluid on the surface and transmitted to the SCSSV via a control line. A pump at the surface, controlled via a control panel, delivers hydraulic fluid under pressure in regulated manner. The control line is arranged inside the annular zone between the production column and the surrounding casing of the well.
The SCSSV automatically closes the production stream in response to one or more well safety conditions that may be detected and/or indicated at the surface. By way of non-limiting example, such conditions include fire on a platform, damage to the wellhead, e.g. as the result of a collision between a truck or a boat and the wellhead, a high or low pressure situation in the flow lines, a high or low temperature situation in the flow lines, or an intervention by an operator.
Such conditions lead to a drop in the hydraulic pressure in the control line, thereby causing a flap to close in such a manner as to block the upward stream of production fluids along the column. In other words, when a dangerous condition or problem occurs at the surface of a well, fluid communication between the tank on the surface and the control line is interrupted. This interrupts the application of hydraulic pressure against the actuator mechanism. The actuator mechanism retracts inside the valve, thereby enabling the flap to close against an annular seat.
Most surface-controlled subsurface safety valves are “normally-closed” valves, i.e. the valve is in its closed position whenever there is no hydraulic pressure. The hydraulic pressure typically acts against a powerful spring and/or a compressed gas via a piston.
In numerous commercially-available valve systems, the power of the spring is exceeded by the hydraulic pressure acting on the piston, thereby causing the piston to move longitudinally. In turn, the piston acts against a flow tube or production tube that is of elongate shape. In this way, the actuator mechanism comprises a piston that is hydraulically actuated and that is longitudinally movable so as to act against the flow tube in order to move it along the column and in front of the flap.
During production, the flap is held in the open position by the force of the piston acting against the end of the flow tube. The hydraulic fluid is pumped into a variable-volume compression chamber and acts against a hermetically sealed zone of the piston. In turn, the piston acts against the flow tube so as to open the flap element in the valve, in selective manner.
Any loss of hydraulic pressure in the control line causes the piston to retract and the flow tube to be actuated. This causes the flap to pivot about a hinge until the valve is in the closed position, e.g. by using a torsion spring and in response to the upwardly-flowing formation fluid.
In this way, the SCSSV can shut-off the production stream in the column when the hydraulic pressure in the control line is released. An example of a safety valve as described above is disclosed for example in FR 2 900 682 in the name of the Applicant.
At the beginning of the operation of a well, typically during its first five to ten years, the pressure of the effluent within the formation ensures that it rises in natural manner. In contrast, as the pressure decreases, it becomes necessary to perform additional operations in order to allow production to continue.
A first known solution consists in raising the safety valve and in propelling a gas downhole using the so-called “gas lift” technique, in order to cause the effluent to rise. Nevertheless, such a method is not satisfactory insofar as it is particularly complex, since it involves removing the safety valve completely.
As an alternative, proposals have also been made to inject an additive towards the effluent-containing formation, which additive is generally a chemical and serves to enhance upward flow of the fluid. It is possible firstly to pass this fluid directly via the control line.
Nevertheless, that presents several drawbacks. Thus, when additive injection is stopped, that necessarily causes the valve to close, since that is the normal position of the valve. Furthermore, when injected into the control line, certain types of additive cannot control the valve in appropriate manner, particularly if they present a high degree of viscosity.
An improvement to the solution described immediately above consists in injecting the additive via a set of ducts that are independent both from the control line and from the production tube. Such an arrangement is described in particular in U.S. Pat. No. 7,712,537.
More precisely, that document provides for injecting the additive via a line that extends axially along the production tube, while being laterally offset relative thereto. The downstream end of that line opens out into an adapter that is itself located downstream from the shutter flap associated with the production tube. Under such conditions, additive can be injected while leaving undisturbed both the flow in the control line and the upward flow of effluent in the production tube.
Nevertheless, that solution presents its own drawbacks. Thus, if the additive is not injected with sufficient pressure, the effluent present downhole is capable of rising directly via the additive injection line, if the downstream safety valve is leaky.
Furthermore, in the event of a major malfunction, e.g. if the wellhead is absent, it is no longer possible for the operator to perform the above-mentioned injection under pressure, such that the effluent can rise along the injection line. Such effluent leakage can lead to catastrophic phenomena of great magnitude, of the “oil spill” type if the effluent is oil.
Publication U.S. Pat. No. 4,022,273 discloses a safety valve including a bypass type injection line that is opened and closed in succession by movement in translation of a sleeve that is provided in the production tube with channels and orifices moving relative to one another so as to face one another or so as to be offset from one another.
Publication U.S. Pat. No. 4,042,033 also discloses a safety valve that includes a ball valve in a production line and a sleeve movable in translation in the production line to open and close a chemical additive injection line in succession. The safety valve is designed so that the production tube and the injection line are opened simultaneously and are then closed when the pressure applied by the fluid becomes less than or equal to the pressure needed for holding the ball valve open.
Publication GB 2,197,011 describes a safety valve including a flap that is tilted when a sleeve moves down inside the production tube, the sleeve having a shoulder that is suitable during downward movement of the sleeve for bearing against a ring provided on a rod that slides in a parallel pipe connecting together the portions upstream and downstream of the flap in order to balance pressures and make it easier to open the flap.
Publication WO 2008/002473 describes a device of the bypass type.